FETAL CEREBRAL, CIRCULATORY, AND METABOLIC RESPONSES DURING HEART-RATE DECELERATIONS WITH UMBILICAL-CORD COMPRESSION

OBJECTIVE: The purpose of this study was to determine the cerebral, ci rculatory, and metabolic responses of the ovine fetus near term to umb ilical cord compression with variable-type fetal heart rate decelerati ons. STUDY DESIGN: Nine fetal sheep, at 0.9 of gestation, were studied before, during, and after umbilical cord occlusion for 1-minute and a gain after repetitive 1-minute cord occlusions every 5 minutes for 1 h our, with resultant fetal heart rate decelerations of similar to 90 be ats/min. Brachiocephalic arterial and sagittal venous blood was analyz ed for oxygen content, blood gases and pH, glucose, and lactate. Cereb ral and upper body blood flow was measured with the microsphere techni que. RESULTS: Umbilical cord occlusion with moderate to severe variabl e-type fetal heart rate deceleration resulted in an immediate drop in arterial Po-2 by similar to 7 torr, an increase in Pco(2) by similar t o 9 torr, and a small but significant increase in lactate levels. Cere bral oxidative metabolism was well maintained but required an increase in fractional oxygen extraction because the variable change in cerebr al blood flow was insufficient to maintain oxygen delivery. A redistri bution of upper body blood flow was evident, with that to the brain an d heart variably maintained or increased whereas that to muscle tissue was markedly decreased. Repetitive umbilical cord occlusion over 1 ho ur resulted in a significant drop in fetal arterial pH, with the acide mia mixed as Pco(2) increased similar to 6 torr, whereas lactate level s increased almost fourfold. CONCLUSION: Although cerebral oxidative m etabolism appears to be well maintained during moderate to severe vari able-type fetal heart rate decelerations with umbilical cord occlusion , the need to increase fractional oxygen extraction and the redistribu tion of blood flow from carcass tissues may contribute to an accumulat ion of lactic acid both within the brain and systemically when such an insult occurs repeatedly.